Method of bonding two bodies together

ABSTRACT

A surface of each of the bodies is coated with a layer of gold. The bodies are placed in a chamber which is evacuated to a pressure of at least 10 3 torr. While maintaining the chamber and its contents at room temperature, the gold layers are brought into contacting relation and a pressure of between 800 psi and 2500 psi is applied to the bodies to bond the gold layers together.

United States Patent 1191 1111 3,921,885

Knox Nov. 25, 1975 METHOD OF BONDING TWO BODIES American WeldingSociety, Welding Handbook, Sec- TOGETHER tion 3, Fifth Edition, Chapter50, pages 50.2-50.4,

American Welding Society, Welding Handbook, Secl l Ass1gnee= RCAC9r119rat19n. New York, tion 4, Fifth Edition, Chapter 74, pages74.10-74.11,

[75] Inventor: Joseph Dale Knox, Princeton, NJ.

221 Filed: June 28, 1973 1966- Sittig et 211., Proceedings lEEE, AMethod for Prepar- [21] Appl 374396 ing and Bonding UltrasonicTransducers Used in High Frequency Digital Delay Lines, 1968, pages 52US. Cl. 228/116; 228/121; 228/208 13751376- [51] Int. Cl. 823K 21/00[58] Field of Search 29/472.7, 472.9, 473.1, Primary Examiner-GranvilleY. Custer, Jr.

29/594, 470.1, 488, 498, 501, 502, 504; Assistant Examiner-James W.Davie 228/115, 116, 121, 208 Attorney, Agent, or Firm-G. H. Bruestle; D.S. Cohen [56] References Cited 57 ABSTRACT UNITED STATES PATENTS Asurface of each of the bodies is coated with a layer 3,131,459 5/1964Allen 29/4727 f gold The bodies are placed in a chamber which is3,252,722 5/1966 Allen 29/504 x evacuated to a pressure of at least -3tom while 3,590,467 7/1971 Chase et a1. 29/4727 maintaining the chamberand its contents at room 3,599,123 8/1971 Krause 29/473.l X

3,791,028 2/1974 Missel 29/4701 x Femperatflre' the gold layers arebrought i 3,798,746 3 1974 Alphouse et a1 29/4701 8 F'?" a P 9 between800 PSI and 2500 ps1 1s apphed to the bod1es to bond the gold lay- OTHERPUBLICATIONS ers together .1. J. Cuomo, l.B.M. Technical DisclosureBulletin, VOL 7, No 3 Aug 1964 3 Claims, 3 Drawmg Figures 0047 SURFACEOF EACH BODY WITH CHROMIUM FILM COAT EACH CHROMIUM FILM WITH ALUMINUMFILM c047 EACH ALUMINUM FILM WITH (sou) FILM PLACE BODIES IN CHAMBERWHICH IS EVACUATED I BRING GOLD LAYERS INTO CONTACTING RELATION ANDAPPLY PRESSURE TO BODIES sheet 10m 3,921,885-

Fig. 1.

COAT SURFACE OF EACH BODY WITH CHROMIUM FILM COAT EACH CHROMIUM FILMWITH ALUMINUM FILM COAT EACH ALUMINUM FILM WITH GOLD FILM PLACE BODIESIN CHAMBER WHICH IS EVACUATED BRING GOLD LAYERS INTO CONTACTING RELATIONAND APPLY PRESSURE TO BODIES US. Patent Nov. 25, 1975 Fig. 2

U.S. Patant Nov. 25, 1975 Sheet20f2 3,921,885-

METHOD or BONDING Two BoDIEs TOGETHER BACKGROUND OF THE INVENTION Thepresent invention relates to a room temperature, relatively low pressurebonding method for bonding together two bodies. More particularly,the-present invention relates to such a bonding method for'bondingtogether two crystal bodies of an acoustic transducer device to providea bond between the bodies which is mechanically strong and which willsatisfactorily transmit high frequency oscillations. i i

Acoustic devices, such as light deflectors, modulators and acousticdelay lines, generally include a transducer body which is capable ofgenerating high frequency oscillations, bonded to a body of a materialwhich utilizes the oscillations for the purpose ofthe' particulardevice. Such bodies are generally of crystalline piezoelectricmaterials. For such acoustic devices, the bond between the bodies mustnot only provide a good mechanical connection between the bodies butmust also be capable of transmitting the high frequency oscillationswith a minimum of loss.

The normal techniques of bonding two bodies together by means of asolder or brazing material are not satisfactory for the acoustic devicesbecause the solders or brazing materials are too lossy with regard tothe transmission of high frequency oscillations. Another method whichhas been used to bond two bodies together is to coat a surface of eachof the bodies with a metal film and fuse the two metal films together bythe application of heat and pressure. However, this method is notsatisfactory for acoustic devices since the temperature to which thebodies are heated during the fusion operation can adversely affect thebodies. Another method which has been used and which can be carried outat room temperature is to coat a surface of each of the bodies with afilm of a soft metal, such as indium, and then fuse the soft metal filmstogether by the application of pressure. However, this method also isnot suitable for high frequency acoustic devices (i.e. microwave delaylines) since the soft metal which has been used is lossy with regard tothe transmission of high frequency oscillations. Therefore, to bond;together the bodies of two acoustic devices, it is desirable to have abonding method which can be carried out under conditions which do notadversely affect the bodies. i.e. at room temperature and relatively lowpressure, and

which provides a bond having good mechanical properties as well as goodhigh frequency oscillation transmission properties.

SUMMARY OF THE INVENTION Two bodies are bonded together by coating asurface of each of the bodies with a layer of gold. The bodies areplaced in a chamber which is evacuated. The gold layers are brought intocontacting relation and a pressure is applied to the bodies sufficientto bond the gold layers together.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a flow chart showing thesteps of the method of the present invention.

FIG. 2 is a cross-sectional view of a device made by the method of thepresent invention.

FIG. 3 is a schematic view of an apparatus suitable for carrying out themethod of the present invention.

2 DETAILED DESCRIPTION Referring initially to FIG. 2, a form of anacoustic de vice made by the method of the present invention'isgenerally designated as 10. The acoustic device 10 comprises a pair ofbodies 12 and 14, of a piezoelectric material, such as lithium niobate,or other acoustic mater ials, such as spinel, paratellurite or highindex glasses. The bodies 12 and 14 each has a surface 120 and 14a,respectively, which is optically polished to a smooth, flat condition.Coated on each of the surfaces 12a andl4a is a layer 16 a'nd'18,respectively, of a metal which adheres well, to the material of thebody. such as chromium, molybdenum or titanium. On each of the metallayers 16 and 18 is a thin layer 20 and 22, respectively, of aluminum.The aluminum layers 20and 22 are preferably of a thickness of 1500 to2500A. Coated on each of the aluminum layers 20 and 22 is a thin layer24 and 26, respectively, of gold. The gold layers 24 and 26 arepreferably of a thickness of 500 to 1000A. The gold layers 24 and 26 arein contacting relation and are fused together by the method of thepresent invention.

As indicated in the flow chart of FIG. 1, to make the acoustic device 10by the method of the present invention, the surfaces 12a and 14a of thebodies 12 and 14 are each first coated with the metal layer 16 and 18,respectively, such as by the well-known technique of evaporation in avacuum. The aluminum layers 20 and 22 are then coated on the metallayers 16 and 18, respectively, and the gold layers 24 and 26 are .thencoated on the aluminum layers 20 and 22, respectively. The aluminumlayers 20 and 22 may be applied by the well-known technique ofevaporation in a vacuum, and the gold layers 24 and 26 may be appliedeither by evaporation in a vacuum or by electroplating.

As shown in FIG. 3, the two bodies 12 and 14 are then placed in achamber 28 which contains a press 30. The bodies 12 and 14 are mountedon the plates 32 and 34 respectively, of the press 30 with the goldlayers 24 and 26 facing each other. The chamber 28 is then evacuated toa pressure of at least 10' torr and preferably to a pressure of 10'torr. The plate 32 of the press 30 is then moved toward theplate 30,either by hydraulic or mechanical'means, until the gold layers 24 and 26are contacting each other. While maintaining the chamber and itscontents at room temperature, a pressure of 800 to I600 psi is appliedto the bodies and maintained for a time to cause the gold layers 24 and26 to bond together. When apressure of 1200 psi is applied to thebodies, fusion of the gold layers 24 and 26 is achieved when thepressure is maintained for about 1 hour. If a lower pressure is used,the time necessary to achieve bonding of the gold layers will be higher,whereas the time is lower if a higher pressure is used.

In the method of the present invention, by bonding the two bodies 12 and14 together in an evacuated chamber, the gold layers 24 and, 26 can befused together at room temperature and at a relatively low pressure sothat the bodies will not be broken or otherwise adversely affected. Themetal layers 16 and 18 merely serve as adhesive layers to achieve goodadhesion of the aluminum layers 20 and 22 to the bodies 12 and 14. Thealuminum layers 20 and 22 serve to provide good alignment between thesurfaces 12a and 14a of the bodies 12 and 14 when the bodies are pressedtogether. However, if desired, the aluminum layers 20 and 22 can beeliminated and replaced with thicker 3 gold layers 24 and 26. If thickergold layers are used, the presssure necessary to achieve bonding of thegold layers should be increased to between about 2000 and 2500 psi.

The method of the present invention not only provides a good mechanicalbond between the bodies 12 and 14, which bond is achieved at roomtemperature and relatively low pressure, but the gold to gold bond alsoprovides for good transmission of high frequency oscillations from oneof the bodies to the other. Although the method of the present inventionhas been described for bonding together two bodies of an acousticdevice, it can also be used to bond together anytwo bodies which may beadversely affected by high temperatures and pressures.

I claim:

1. A method of bonding together two bodies of an acoustic materialcomprising the steps of applying a layer of gold on a surface of each ofthe bodies,

placing the bodies in a chamber.

evacuating said chamber to a pressure of at least 10' torr, bringing thegold layers into contacting relation, and vwith the bodies being at roomtemperature applying a pressure of 800 to l600 psi to said bodies for atime sufficient to bond the gold layers together. I

2. A method in accordance with claim 1 including providing a layer ofaluminum over each of said surfaces of the bodies and coating the goldlayer on the aluminum layer.

3. The method in accordance with claim 2 including coating each of saidsurfaces of the bodies with a metal adhesive layer selected from thegroup consisting of chromium, molybdenum and titanium and coating thealuminum layers on the adhesive layers.

1. A METHOD OF BONDING TOGETHER TWO BODIES OF AN ACOUSTIC MATERIALCOMPRISING THE STEPS OF APPLYING A LAYER OF GOLD ON A SURFACE OF EACH OFTHE BODIES, PLACING THE BODIES IN A CHAMBER, EVACUATING SAID CHAMBER TOA PRESSURE OF AT LEAST 10**-3 TORR, BRINGING THE GOLD LAYERS INTOCONTACTING RELATION, AND WITH THE BODIES BEING AT ROOM TEMPERATUREAPPLYING A PRESSURE OF 800 TO 1600 PSI TO SAID BODIES FOR A TIMESUFFICIENT TO BOND THE GOLD ALYERS TOGETHER.
 2. A method in accordancewith claim 1 including providing a layer of aluminum over each of saidsurfaces of the bodies and coating the gold layer on the aluminum layer.3. The method in accordance with claim 2 including coating each of saidsurfaces of the bodies with a metal adhesive layer selected from thegroup consisting of chromium, molybdenum and titanium and coating thealuminum layers on the adhesive layers.